cmd/anubis: cache DNSBL hits in a DecayMap

Signed-off-by: Xe Iaso <me@xeiaso.net>

1 files changed, 57 insertions, 0 deletions

diff --git a/cmd/anubis/decaymap.go b/cmd/anubis/decaymap.go
new file mode 100644
index 0000000..bf55d2a
--- /dev/null
+++ b/cmd/anubis/decaymap.go
@@ -0,0 +1,57 @@
+package main
+
+import (
+	"sync"
+	"time"
+)
+
+func zilch[T any]() T {
+	var zero T
+	return zero
+}
+
+type DecayMap[K, V comparable] struct {
+	data map[K]DecayMapEntry[V]
+	lock sync.RWMutex
+}
+
+type DecayMapEntry[V comparable] struct {
+	Value  V
+	expiry time.Time
+}
+
+func NewDecayMap[K, V comparable]() *DecayMap[K, V] {
+	return &DecayMap[K, V]{
+		data: make(map[K]DecayMapEntry[V]),
+	}
+}
+
+func (m *DecayMap[K, V]) Get(key K) (V, bool) {
+	m.lock.RLock()
+	value, ok := m.data[key]
+	m.lock.RUnlock()
+
+	if !ok {
+		return zilch[V](), false
+	}
+
+	if time.Now().After(value.expiry) {
+		m.lock.Lock()
+		delete(m.data, key)
+		m.lock.Unlock()
+
+		return zilch[V](), false
+	}
+
+	return value.Value, true
+}
+
+func (m *DecayMap[K, V]) Set(key K, value V, ttl time.Duration) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	m.data[key] = DecayMapEntry[V]{
+		Value:  value,
+		expiry: time.Now().Add(ttl),
+	}
+}